ucs2len

Rename boot1's wcslen to ucs2len, which we can't use in userland
because wchar in userland is unsigned, not short. Move it into
efichar.c. Also spell '* 2' as '* sizeof(efi_char)' and add 1 for the
trailing NUL to transition the FreeBSD boot env vars to being NUL
terminated on the same line...

Sponsored by: Netflix